This application is based on application No. MI97A 02890 filed in Italy and U.S. Provisional Application No. 60/083,799 filed on May 1, 1998, the content of which is incorporated hereinto by reference.
This invention relates to a solid combustible composition comprising a first portion consisting of an urban solid waste, a second portion consisting of elastomeric material and a third portion consisting of a non-elastomeric polymeric material.
Up to now many methods have been proposed to destroy and/or recover, at least partially, urban solid wastes, out of use tyres and plastic packaging materials.
However, the problem is very complex owing to the fact that the nature and composition of the wastes varies from place to place and from day to day, and owing to the presence of a perishable organic portion.
Some of the methods proposed up today imply the removal of the perishable organic phase from the solid products which are then dried, crumbled and agglomerated. Generally this agglomeration is performed via compression into granules or bricks.
According to the Applicant""s perception, a drawback of these methods is that the caloric power of the obtained solid combustible material varies from batch to batch. Another drawback is that some kinds of boilers and burners, such as the instantaneous combustion ones, can not be fed with a combustible agglomerated into granules or bricks. Still another drawback is that the granule and brick preparation comprises some steps, such as the compression step, involving a certain energetic expenditure and, therefore, a cost increase which renders uneconomical the above known methods.
Now a combustible composition has been found which can be produced avoiding the agglomerate formation.
According to a first aspect, this invention relates to a solid combustible composition comprising a first portion consisting of an urban solid waste, a second portion consisting of an elastomeric material and a third portion consisting of a non-elastomeric polymeric material, characterised in that it has an apparent density lower than 0.6 g/cm3.
According to a second aspect, the first portion consisting of urban solid wastes is suitably crumbled and dried separately until it has a moisture contents xe2x89xa610%. Preferably, also the two other portions are suitably crumbled. The amount of each of the three portions is not critical and varies according to the caloric power pre-selected for the composition of this invention.
Typically, a solid combustible composition of the present invention comprises a first portion consisting of an urban solid waste, a second portion consisting of an elastomeric material and a third portion consisting of a non-elastomeric polymeric material and is characterised in that:
the urban solid waste has a moisture contents xe2x89xa610%,
each of the three portions is crumbled separately in a controlled way,
the three crumbled portions are mixed together so as to obtain a mixture having a selected caloric power.
Typical examples of elastomeric materials useful to prepare the composition of this invention are the out of use tyres.
Typical examples of non-elastomeric polymeric materials useful to prepare the composition of this invention are the packages and the wrappings made of thermoplastic and/or thermosetting materials. Typical examples of thermoplastic materials used in the packing field are PE, LDPE, HDPE, PP, PET, polystyrene, ethylene/xcex1-olefines C4-C12 copolymers, vinyl-polymers and copolymers and the like.
There are no particular limitations to the percentage ratios of these portions; these ratios being mainly predetermined depending on the caloric power pre-selected for the combustible composition of this invention. Typically, the composition of this invention shall comprise 40 to 80% by weight of an urban solid waste, 10 to 50% by weight of an elastomeric material and 10 to 50% by weight of a non-elastomeric polymeric material. Preferably it shall comprise 60 to 80% by weight of an urban solid waste, 10 to 30% by weight of an elastomeric material and 10 to 30% by weight of a non-elastomeric polymeric material.
Typically the average size of urban solid wastes in the combustible composition of this invention is xe2x89xa660 mm and, preferably xe2x89xa625 mm. The average size of the elastomeric material is xe2x89xa610 mm, preferably xe2x89xa65 mm and, still, more preferably xe2x89xa61 mm. The average size of the non-elastomeric polymeric material is xe2x89xa640 mm and, preferably xe2x89xa615 mm.
Preferably the apparent density of the combustible composition of this invention is xe2x89xa60.4 g/cm3. Still more preferably it is of from 0.3 and 0.1 g/cm3.
The caloric power of the combustible composition of this invention will be chosen by a person skilled in the art depending on the thermal requirements of the plant used, by suitably selecting the amount by weight of each portion according to its own caloric power.
Generally, it will be of 4,000 to 6,000 Kcal/kg. Still more preferably it will be of 4,500 to 5,500 Kcal/kg.
The inventors perceived that the solid combustible composition of this invention is particularly advantageous when the average size of the elastomeric material is of about 1 mm because it can thus be used to feed also instantaneous combustion plants. That means, those plants where the combustible is burned almost completely in a very short time, typically in less than 10 seconds, preferably in less than 3 seconds.
The method of this invention implies the trituration of urban solid wastes after separation of the perishable organic portion, as well as the iron and aluminium materials.
It further implies the trituration of the plastic materials, preferably together with the said urban solid waste.
Urban solid wastes and tritured plastic materials are conveyed to a hot-air drier and then to a mill where they undergo a further crushing.
The tyres, in their turn, are crushed and deprived of the iron material. In case of huge tyres, before crushing it is preferable to remove the bead.
A second aspect of this invention consists, therefore, of a process where:
a) an urban solid waste is treated to remove
a1) the perishable organic portion via screening,
a2) the iron materials by means of a magnetic separator,
a3) aluminium by means of an eddy-current magnet,
b) the thus obtained urban solid portion is tritured,
c) a waste material consisting of a non-elastomeric polymeric material is tritured,
d) the above portions of tritured urban solid wastes and non-elastomeric polymeric material are dried until their moisture content is equal to or lower than 10%,
e) the above portions are ground into bits,
f) an elastomeric material is ground into bits and deprived of any iron material associated thereto,
g) the above bits of urban solid wastes, non-elastomeric polymeric material and elastomeric material are mixed together in a weight ratio which is predetermined in view of the desired caloric power.
According to a further aspect, this invention relates to a process for preparing a solid combustible composition characterised in that non-agglomerated bits of urban solid wastes, non-elastomeric polymeric material and elastomeric material are mechanically mixed together in a weight ratio so as to give a solid combustible composition having a caloric power of from 4,000 to 6,000 Kcal/Kg; preferably, of from 4,500 to 5,500 Kcal/Kg.